INSECTICIDES AND EQUIPMENT FOR CONTROLLING INSECTS 17 



Caution. — Lead arsenate is a very poisonous compound and 

 should be stored in plainly labeled containers away from all food 

 products. 



Both lead and arsenic residues on treated plants are poisonous. The 

 Federal tolerance for lead on apples and pears is now 0.05 grain per 

 pound and for arsenic it is 0.025 grain of As 2 3 per pound. 



LEAD ARSENATE (BASIC ) 



Chemically, basic lead arsenate is lead hydroxy arsenate 

 (Pb 4 (PbOH) (As0 4 ) 3 ). It should contain about 23 percent of total 

 arsenic pentoxide (As 2 5 ) and less water-soluble arsenic than the 

 equivalent of 0.5 percent of arsenic pentoxide. 



Like the much more commonly used acid lead arsenate, this ma- 

 terial is a white powder which is colored pink when marketed as an 

 insecticide to denote that it is a poison. Its use is virtually limited 

 to particular areas on the Pacific coast and in eastern peach orchards, 

 for certain chewing insects, where acid lead arsenate causes plant 

 injury. It is less effective in controlling insects than is the acid 

 form! Normally it is used at a rate of about -i to 6 pounds to 100 

 gallons of water. 



Caution. — Like acid lead arsenate, this material is toxic to man 

 and higher animals, and should be stored in a safe place in clearly 

 labeled packages. 



The spray-residue tolerances for acid lead arsenate, as given above, 

 apply also to basic lead arsenate. 



LIQUID LIME-SULFUR AND DRY LIME-SULFUR 



As the name implies, lime-sulfur is made from lime and sulfur. 

 A complex mixture containing principally calcium polysulfides, it 

 may be purchased in concentrated solution or as a dry powder, or 

 it may be made on the farm. It is marketed in concentrated form 

 as a deep amber-colored liquid, or as a yellow-orange powder. It 

 is applied in the dilute form and is ill-smelling and irritating to the 

 user. 



Liquid lime-sulfur is used chiefly as a scalicide and a fungicide on 

 fruit trees and woody shrubs. It is used extensively for the control 

 of the potato psylla in the Western States and is also valuable for 

 the control of the peach twig borer, pear psylla. and blister mite. 

 A- a scalicide it has been displaced in some localities by lubricating- 

 oil sprays. When used in the dormant season to control scale inserts 

 it is applied at a strength of 10 to 14 gallons of the liquid concentrate 

 in 100 gallons of spray. As a fungicide and as a spray for the com- 

 mon red spider and some other mites on plant foliage it is usually 

 diluted to a strength of 2 gallons in 100 gallons of spray. 



For control of the cyclamen mite on chrysanthemums ami snap- 

 dragons, a lime-sulfur spray consisting () f l to 2 quarts to LOO gallons 

 of water with the addition of :; j pint (l 1 ^ cupfuls) of a spreader — 

 sodium oleyl sulfate containing a synthetic resinous sticker — lias 

 proved effective. This spray has the advantage of not staining the 

 foliage as does lime-sulfur solution without the spreader. 



For some purposes dry lime-sulfur may be substituted for liquid 

 lime-sulfur at the rate of 1 pounds lor 1 gallon of the liquid. On 



